1. Field of the Invention
The present invention relates to a fuel cell metal separator that makes up part of a fuel cell in which plural electrolyte electrode assemblies, each comprising a pair of electrodes provided on both sides of an electrolyte, are stacked, as well as to a noble metal coating method for such a metal separator.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA), which includes an anode and a cathode provided on both sides of a polymer electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between a pair of separators to thereby make up a unit cell (power generating cell) for generating electricity.
With this type of fuel cell, when used in an automotive vehicle, normally, a predetermined number (e.g., several tens to several hundreds) of such unit cells are stacked together to form a fuel cell stack.
At this time, on surfaces of the separators, reactant gas flow fields are formed through which a reactant gas flows along surfaces of the electrodes. For this purpose, in the case that metal separators are used as the separators, convex portions that abut against the electrode surfaces and concave portions that form the reactant gas flow fields are provided therein by press-forming the metal separators in wave-like shapes.
In the above metal separators, it is required to maintain good conductivity, corrosion resistance, and abrasion resistance. For this reason, coating layers of gold are formed on surfaces of the metal separators.
For example, in Japanese Laid-Open Patent Publication No. 2010-077464, a method is disclosed in which convex portions of a plated member are brought into contact with a liquid holding member that is immersed in a plating bath, and electrolytic plating is carried out selectively on top surface parts of the convex portions. In this method, plating is performed in a Au plating bath, with a pulse current having the maximum electric current density of 20 to 260 A/dm2 and the average electric current density of 5 to 26 A/dm2.